1. Field of the Invention
The invention relates to a semiconductor element and a manufacturing method thereof and, more particularly, to a technique for electrically separating two electrodes.
2. Description of the Related Arts
A semiconductor laser whose response speed is raised by unitedly integrating an intensity modulator and a laser diode has been known. For example, a semiconductor integrated element of a ridge waveguide type including an EA (Electro-Absorption type) modulator, a DFB (Distributed Feedback type) laser, and a ridge type optical waveguide connecting them has been disclosed in JP-A-2006-351818.
As shown in FIG. 12, an electrode 60 of an EA modulator (hereinbelow, referred to as “EA portion”) 52 and an electrode 62 of a laser (hereinbelow, referred to as “LD portion”) 54 are formed on the surface of a semiconductor integrated element 50 of the ridge waveguide type, respectively. The electrodes 60 and 62 are formed by the following steps. First, a passivation film (for example, SiO2 film) for surface protection is formed on the whole surface of a wafer. Further, an electrode material (for example, Au) is evaporation-deposited on the passivation film. Finally, areas other than areas which become the electrodes in formed electrode layers are removed by dry etching having an orientation, thereby forming the electrode 60 of the EA portion 52 and the electrode 62 of the LD portion 54.
However, the ridge waveguide type semiconductor integrated element which is manufactured by the foregoing steps in the related has the following factors of deteriorating a manufacturing yield.
FIGS. 13A and 13B are cross sectional views of the ridge waveguide type semiconductor integrated element 50 taken along the line a-a′ in FIG. 12. FIG. 13A shows a cross sectional structure after the electrodes were evaporation-deposited. FIG. 13B shows a cross sectional structure after an electrode pattern was formed. Since passivation films 68 serving as insulating films (protecting films) are isotropically formed on an upper surface and a side surface of a waveguide 56 by a CVD (Chemical Vapor Deposition), in an upper periphery 74 of the waveguide 56, a thickness of passivation film 68 is thicker than those of the other portions as shown in FIG. 13A.
According to the foregoing manufacturing method in the related art, since the electrode material is directly evaporation-deposited onto the passivation film 68, if a dry etching having an orientation such as ion milling or the like is used to form the electrode pattern, as shown in FIG. 13B, in a side wall of the waveguide 56, a portion where the thickness of passivation film 68 changes becomes a shadow of an ion beam and there is a case where an electrode layer 66 formed in such a portion is not perfectly removed. Similarly, there is also a case where in bottom corner portions of grooves formed on both sides of the waveguide, a part of the electrode layer 66 is not removed but remains.
That is, according to the ridge waveguide type semiconductor integrated element 50, since the EA portion 52 and the LD portion 54 are coupled by the groove formed by concave/convex-shaped insulating walls along the waveguide 56 of the ridge type, if the electrode material is directly evaporation-deposited onto a groove portion of a separating portion 58 for separating the EA portion 52 and the LD portion 54 in accordance with the manufacturing steps in the related art, there is a case where in the concave/convex-shaped insulating walls which form the grooves, the electrode layer 66 formed in the portion which becomes the shadow of the ion milling or the like is not perfectly removed. There are, consequently, such problems that a separation resistance of the electrode 60 of the EA portion 52 and the electrode 62 of the LD portion 54 decreases, the response speed of the semiconductor laser decreases, and the manufacturing yield deteriorates.